1. Field of the Invention
The present invention relates to neurostimulation or drug infusion devices, and more particularly relates to techniques for activating or deactivating a neurostimulator or drug delivery system based on time-of-day or biological rhythmic patterns.
2. Description of Related Art
Neurostimulation devices and drug delivery devices are now capable of treating any number of disorders as well as symptoms of disorders. In the context of neurostimulators, an electrical lead having one or more electrodes is typically implanted near a specific site in the brain or spinal cord of a patient. The lead is coupled to a signal generator which delivers electrical energy through the electrodes to nearby neurons and neural tissue. The electrical energy delivered through the electrodes creates an electrical field causing excitation of the nearby neurons to directly or indirectly treat the neurological disorder or a symptom of the disorder. In the context of a drug delivery system, a catheter coupled to a pump is implanted near a treatment site in the brain or spinal cord. These systems are commonly implanted within the body and are operated by a power source such as a battery.
Recent advances have allowed these neurostimulation devices and drug delivery systems to adjust treatment in accordance with the patient's needs. Generally, these systems incorporate a sensor for sensing a physical or chemical characteristic of the body and generating a sensor signal in response. The sensor signal may then be used to adjust the treatment therapy. U.S. Pat. No. 5,716,377, for example, discloses a method of treating movement disorders by closed loop brain stimulation.
These systems, however, provide electrical stimulation or drug delivery regardless of the time of day or the patient's needs. These system are capable of adjusting the treatment but are incapable of recognizing periods when a patient does not require any therapy. For example, patients often will not require any stimulation or drug therapy during periods when he/she is resting or sleeping. During such time periods, the manifestation of the movement disorder may be minimal or even non-existent. This is often the case for patients suffering from movement disorders and certain types of pain.
Stimulation or drug delivery at times when it is not required by the patient unnecessarily depletes the battery or the drug reserve which is often implanted within the body. This requires more frequent surgical procedures to replace the spent battery or more frequent drug injections. An even greater concern with continuous therapy systems is that the patient may develop a higher tolerance to the treatment, thereby requiring higher dosage or stronger stimulation to achieve the desired result.
Often, physicians will request the patient to turn off his/her neurostimulator at night. This requires the patient or care giver to manually turn the device off at night before falling asleep and turn on the device after waking up the next day. However, after the neurostimulator is turned off but before the patient has fallen asleep, symptoms of movement disorders, illnesses or other maladies (such as tremor) or pain often return, thereby rendering sleep difficult. Accordingly, there remains a need in the art for automatically shutting off the electrical stimulation or drug delivery during periods when the patient does not require treatment therapy.